Phytoplankton cell lysis associated with polyunsaturated aldehyde release in the Northern Adriatic Sea.

Diatoms are able to react to biotic and abiotic stress, such as competition, predation and unfavorable growth conditions, by producing bioactive compounds including polyunsaturated aldehydes (PUAs). PUAs have been shown to act against grazers and either enhance or inhibit the growth of different phytoplankton and bacteria both in culture and in the field. Presence of nanomolar concentrations of dissolved PUAs in seawater has been reported in the North Adriatic Sea (Mediterranean), suggesting that these compounds are released in seawater following diatom cell lysis.

Insights into the transcriptome of the marine copepod Calanus helgolandicus feeding on the oxylipin-producing diatom Skeletonema marinoi.

Diatoms dominate productive regions in the oceans and have traditionally been regarded as sustaining the marine food chain to top consumers and fisheries. However, many of these unicellular algae produce cytotoxic oxylipins that impair reproductive and developmental processes in their main grazers, crustacean copepods. The molecular mode of action of diatoms and diatom oxylipins on copepods is still unclear.

Copepod population-specific response to a toxic diatom diet.

Diatoms are key phytoplankton organisms and one of the main primary producers in aquatic ecosystems. However, many diatom species produce a series of secondary metabolites, collectively termed oxylipins, that disrupt development in the offspring of grazers, such as copepods, that feed on these unicellular algae. We hypothesized that different populations of copepods may deal differently with the same oxylipin-producing diatom diet.

Molecular evidence of the toxic effects of diatom diets on gene expression patterns in copepods.

Background: Diatoms are dominant photosynthetic organisms in the world's oceans and are considered essential in the transfer of energy through marine food chains. However, these unicellular plants at times produce secondary metabolites such as polyunsaturated aldehydes and other products deriving from the oxidation of fatty acids that are collectively termed oxylipins. These cytotoxic compounds are responsible for growth inhibition and teratogenic activity, potentially sabotaging future generations of grazers by inducing poor recruitment in marine organisms such as crustacean copepods.

Teratogenic effects of diatom metabolites on sea urchin Paracentrotus lividus embryos.

The diatom-derived polyunsaturated aldehydes (PUAs), 2-trans,4-trans-decadienal, 2-trans,4-trans-octadienal, 2-trans,4-trans,7-octatrienal, 2-trans,4-trans-heptadienal, as well as tridecanal were tested on early and later larval development in the sea urchin Paracentrotus lividus. We also tested the effect of some of the more abundant diatom polyunsaturated fatty acids (PUFAs) on development, in particular 5,8,11,14,17-eicosapentaenoic acid (EPA), one of the main precursors of diatom PUAs, as well as 4,7,10,13,16,19-docosahexaenoic acid (DHA), 6,9,12,15-octadecatetraenoic acid (stearidonic acid), 6,9,12-octadecatrienoic acid (gamma-linolenic acid) and 9,12-octadecadienoic acid (linoleic acid). PUAs blocked sea urchin cell cleavage in a dose dependent manner and with increasing chain length from C7 to C10 PUAs, with arrest occurring at 27.

Toxigenic effects of diatoms on grazers, phytoplankton and other microbes: a review.

Traditionally, diatoms have been regarded as providing the bulk of the food that sustains the marine food chain and important fisheries. However, this view was challenged almost two decades ago on the basis of laboratory and field studies showing that when copepods, the principal predators of diatoms, feed on certain diatom diets, they produce abnormal eggs that either fail to develop to hatching or hatch into malformed (i.e.

High plasticity in the production of diatom-derived polyunsaturated aldehydes under nutrient limitation: physiological and ecological implications.

Diatoms have evolved a silicified cell wall that provides an efficient barrier against herbivores. These microalgae also produce chemical compounds such as polyunsaturated aldehydes (PUAs) that can potentially impair recruitment and cause malformations in the offspring of such grazers. We measured silica content as an indication of cell wall thickness, organic nutrient cell quotas, PUAs and polyunsaturated fatty acid cell content in Skeletonema marinoi grown under N-, P- and Si-limitation in continuous cultures.

Aldehyde-encapsulating liposomes impair marine grazer survivorship.

In the last decade, there has been an increased awareness that secondary metabolites produced by marine diatoms negatively impact the reproductive success of their principal predators, the copepods. Several oxylipins, products of the enzymatic oxidation of fatty acids, are produced when these unicellular algae are damaged, as occurs during grazing. In the past, the dinoflagellate Prorocentrum minimum, which does not produce the oxylipin 2-trans,4-trans-decadienal (DD), has been used as a live carrier to calculate daily ingestion rates of this molecule by copepod crustaceans.

LOX-induced lipid peroxidation mechanism responsible for the detrimental effect of marine diatoms on zooplankton grazers.

Some marine diatoms negatively affect the reproduction of dominant zooplankton grazers such as copepods, thus compromising the transfer of energy through the marine food chains. In this paper, the metabolic mechanism that leads to diatom-induced toxicity is investigated in three bloom-forming microalgae. We show that copepod dysfunctions can be induced by highly reactive oxygen species (hROS) and a blended mixture of diatom products, including fatty acid hydroperoxides (FAHs); these compounds display teratogenic and proapoptotic properties.

Age and nutrient limitation enhance polyunsaturated aldehyde production in marine diatoms.

Skeletonema marinoi produces 2,4-heptadienal, 2,4-octadienal, and 2,4,7-octatrienal, the latter only in traces. In nutrient-replete cultures, the production of potentially defensive polyunsaturated aldehydes (PUA) increases from the exponential to the stationary phase of growth from 1.2 fmol cell(-1) (+/-0.

Giant liposomes as delivery system for ecophysiological studies in copepods.

Giant liposomes are proposed as a potential delivery system in marine copepods, the dominant constituent of the zooplankton. Liposomes were prepared in the same size range as the food ingested by copepods (mean diameter of about 7 microm). The encapsulation of a hydrophilic and high molecular mass fluorescent compound, fluorescein isothiocyanate-dextran (FitcDx), within the liposomes provided a means of verifying copepod ingestion when viewed with the confocal laser-scanning microscope.

A stress surveillance system based on calcium and nitric oxide in marine diatoms.

Diatoms are an important group of eukaryotic phytoplankton, responsible for about 20% of global primary productivity. Study of the functional role of chemical signaling within phytoplankton assemblages is still in its infancy although recent reports in diatoms suggest the existence of chemical-based defense strategies. Here, we demonstrate how the accurate perception of diatom-derived reactive aldehydes can determine cell fate in diatoms.

The role of complex lipids in the synthesis of bioactive aldehydes of the marine diatom Skeletonema costatum.

Diatoms are unicellular plants broadly present in freshwater and marine ecosystems, where they play a primary role in sustaining the marine food chain. In the last 10 years, there has been accumulating evidence that diatoms may have deleterious effects on the hatching success of zooplankton crustaceans such as copepods, thus affecting dynamics of planktonic populations and limiting secondary production. At the molecular level, failure to hatch is ascribed to the presence of a family of inhibitory oxylipins, which we propose to collectively name polyunsaturated short-chain aldehydes (abbreviated here as PUSCAs).

Aldehyde suppression of copepod recruitment in blooms of a ubiquitous planktonic diatom.

The growth cycle in nutrient-rich, aquatic environments starts with a diatom bloom that ends in mass sinking of ungrazed cells and phytodetritus. The low grazing pressure on these blooms has been attributed to the inability of overwintering copepod populations to track them temporally. We tested an alternative explanation: that dominant diatom species impair the reproductive success of their grazers.

A marine diatom-derived aldehyde induces apoptosis in copepod and sea urchin embryos.

The diatom-derived aldehyde 2-trans-4-trans-decadienal (DD) was tested as an apoptogenic inducer in both copepod and sea urchin embryos, using terminal-deoxynucleotidyl-transferase-mediated dUTP nick-end labelling (TUNEL), DNA fragmentation profiling (laddering) and an assay for caspase-3 activity. DD induced TUNEL positivity and DNA laddering, but not caspase-like activation, in copepod embryos spawned by females fed for 10-15 days the diatom diet Thalassiosira rotula Meunier (in vivo), or when newly spawned eggs were exposed for 1 h to 5 micro g ml(-1) DD (in vitro). To our knowledge, this is the first time that evidence for an apoptotic process in copepods has been obtained by cytochemical (TUNEL) and biochemical (DNA fragmentation) approaches.

Bioactive aldehydes from diatoms block the fertilization current in ascidian oocytes.

The effects of bioactive aldehydes from diatoms, unicellular algae at the base of the marine food web, were studied on fertilization and early development processes of the ascidian Ciona intestinalis. Using whole-cell voltage clamp techniques, we show that 2-trans-4-trans-decadienal (DD) and 2-trans-4-cis-7-cis-decatrienal (DT) inhibited the fertilization current which is generated in oocytes upon interaction with the spermatozoon. This inhibition was dose-dependent and was accompanied by inhibition of the voltage-gated calcium current activity of the plasma membrane.

Use of the confocal laser scanning microscope in studies on the developmental biology of marine crustaceans.

Confocal Laser Scanning Microscope techniques have been applied to study the developmental biology of marine copepods and decapod larvae. The lipophylic probes DiI and DiOC(6) were used to study both the external and internal morphology of these crustaceans, whereas the same DiOC(6) and the specific nuclear probe Hoechst 33342 were used to study embryonic development of copepods in vivo. To distinguish viable from non-viable copepod embryos, the vital dye dichlorodihydrofluorescein diacetate (H(2)DCFDA) was used.